From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Cause of popping noises in the silencer of 40/50 HP cars when the throttle is shut.
| Identifier | ExFiles\Box 38\4\ Scan033 | |
| Date | 1st June 1921 | |
| To R.{Sir Henry Royce} from Hs.{Lord Ernest Hives - Chair} c. to CJ. c. to BN.{W.O. Bentley / Mr Barrington} c. to E.{Mr Elliott - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} c. to BY.{R.W. Bailey - Chief Engineer} c. to EP.{G. Eric Platford - Chief Quality Engineer} c. to EWT. for R.R.Inc. attention of OY. X3436 Hel/LGI.6.21. X.3436 - RE. POPPING IN THE SILENCER. X.4305 - We periodically receive complaints from customers with regard to popping in the silencer when the throttle is shut. We have carried out tests in order to see whether anything further can be done to overcome this fault on 40/50 H.P. cars. We find that the usual one or two explosions which we get when the throttle is shut are caused by the following conditions:- When the car is running normally with the throttle open, there is always a quantity of liquid petrol clinging to the walls of the induction pipe. When the throttle is shut this petrol is then drawn into the cylinders and mixes with air which leaks in through the valve guides or throttle or through the exhaust system. When the engine is running with the throttle shut there is a high vacuum in the cylinder so that when the exhaust valve opens the cylinder is filled with gas or air from the exhaust system. We find that the reason the explosions are very much worse with the cut-out open is that air can more easily get into the cylinders. The ignition which starts these explosions comes, in the first place, from the magneto or battery ignition. This ignition fires a weak charge in the cylinders which is burning when the exhaust valve opens. A contd:- | ||